A generator typically includes a shaft and rotor body supported by the shaft. The rotor body defines a number of poles, which vary in number depending on the design of the generator. For example, the speed at which the shaft rotates and frequency of electric current to be produced would impact the number of poles used in the generator. In a generator, copper wire is wound along the poles on the rotor body and referred to as the winding. In most large generators, for example, such as used in power generation plants and other similar generator applications, the cooper wire can be formed as flat, stiff, coiled copper bars. In some cases, the copper winding is about 1 by 0.25 inches in cross-section, as one non-limiting example. These coils forming the winding are often referred to as the conductors.
The winding is designed to form a complete circuit from a first pole to the last pole. Because the winding is formed from a stiff material in these large generators, the winding ends are connected between adjacent poles with conductive jumpers known as rotor pole crossovers.
As noted in commonly assigned U.S. Pat. No. 5,111,097, the disclosure which is hereby incorporated by reference in its entirety, rotor pole crossovers are designed in many shapes and sizes and change in design as the generator design requirements dictate. For example, some rotor pole crossovers have been designed as rings that encircle the shaft. Other rotor pole crossovers are designed as short crossovers in the form of flat plates or reverse S-shapes, which are oriented to lie axially relative to the rotor shaft. During generator operation, large centrifugal forces are exerted on the winding and rotor pole crossover, for example, by daily starts and stops to accommodate peak on and off electrical generation demands, and as a result, the rotor pole crossovers undergo stressful cyclic duty. If rotor pole crossovers lack flexibility, they crack and cause a loss in the generator electrical field.
A cracked rotor pole crossover can be repaired by removing the end plate and retaining ring on a generator, and replacing the cracked rotor pole crossover with a new crossover. The new rotor pole crossover is fitted into its proper position and secured into the coil position using brazed scarf or lap joints, for example, such as explained in the '097 patent. The retaining ring and end plate are then reattached. Some laminated rotor pole crossovers have been proposed as replacements for a number of crossovers. These replacement crossovers typically have an extended U-shaped segment (also referred to as an omega depending on its design). Two leg extensions connect to the U-shaped segment and connect to the winding ends via respective lap or scarf joints at the free ends of the legs. A laminated crossover is discussed in the background section of the '097 patent. A laminated crossover differs from flat plates of reverse S-shaped crossovers because the installed, laminated crossover extends radially outward with respect to the shaft, as opposed to being oriented axially with respect to the shaft. Unfortunately, a laminated rotor pole crossover usually cannot be installed axially. If lap joints are connected to the winding end, any attempt to rotate the laminated rotor pole crossover for axial orientation would exert a greater load on the laminations and they would buckle. Cracking would still be a problem.
The '097 patent proposes a rotor pole crossover that can be oriented axial relative to the shaft of the generator, while having greater flexibility and reducing stress. This improved crossover has a variable thickness to create flexibility, and has an extended, substantially U-shaped segment from which two legs curve outwards. This rotor pole crossover is thinned in one direction relative to its leg thickness, but thickened in another direction to create flexibility and reduce stress. It maintains a constant cross-sectional area for proper electrical conduction.
As shown in FIG. 5 of the '097 patent, the rotor pole crossover disclosed in that patent was designed for connection into coil no. 6. FIG. 5 illustrates that there is ample space for a crossover design having an extended U-shaped segment that is long compared to its width.
There are some instances, however, when a rotor pole crossover has to be connected into an area having a much smaller space than that disclosed in the '097 patent. For example, if the rotor pole crossover must be connected to the first coil shown at right of FIG. 5, there is little room for a rotor pole crossover as disclosed in the '097 patent. This can be a problem with numerous older generation generators. Also, laminated rotor pole crossovers are not practical because they are not installed axially. Even if sized correctly to be connected to the first coil, any rotor pole crossover design must also be flexible. Longer rotor pole crossovers, such as disclosed in the '097 patent, have enhanced flexibility because of their length, but crossovers limited in size would not have as much inherent flexibility even if the crossover included thickened and thinned sections.